This invention relates to a phenol-aldehyde resin.
In a particular aspect this invention relates to a resin useful as a cold-set binder for cores and molds used in the foundry industry.
It is known from J. Robins, U.S. Pat. Nos. 3,676,392; 3,409,579; and 3,485,797 to provide rapid curing binders for foundry aggregates. The binders are phenol-aldehyde resins which are reactive with isocyanates or prepolymers or polyurethanes. According to Robins, the foundry aggregate is mixed with the resin to which has been added a weak amine curing agent. This mixture is mixed with the isocyanate or polyurethane, then placed in a molding box or core box and after a short curing time, the mold or core is firm enough to be removed. This process makes possible a high production rate from a limited number of molds or core boxes, which are often very expensive and difficult to make.
In U.S. Pat. No. 3,485,797, Robins discloses a resin made by reacting an aldehyde with a phenol at a mole ratio greater than 1 in the presence of a catalyst selected from organic carboxylic salts of lead, zinc, stannous tin, iron, lithium, manganese, cobalt, copper and calcium. Of these salts, lead and zinc produced a resin containing between 5 and 10% of free formaldehyde (based on the original) whereas the remaining (except for tin for which no data are disclosed) produced a resin containing from 11 to 34% of the original formaldehyde in unreacted form. These resins are described as being a mixture of dimethylol compounds having dimethylene ether linkages and methylene linkages, the former being predominant. During the reaction, water is removed continuously as an azeotrope with, e.g. aliphatic, aromatic and halogenated hydrocarbons, ethers, esters and ketones. These resins can be cross-linked by heating or by the addition of acidic compounds such as BF.sub.3, ZnCl.sub.2, SnCl.sub.4 or hydrogen acids such as sulfuric and sulfonic acids.
These binders have been very successful, but there have been some problems associated with them. The principal problems involve poor solubility of the resins in organic solvents and the lead catalyst, which is generally preferred for preparing them, remains in the resin where it forms a toxic residue, thus becoming an industrial hygiene problem.